Method of and apparatus for coating paper



April 30, 1940. N. .OBENSHAIN ET AL METHOD OF AND APPARATUS FOR COATINGPAPER Filed July 16, 1936 INVENTORS 0E5 NOEL IVE/EH7 ATTORNEY v I.Patented Apr. 30, 1940 UNITED STATES METHOD OF AND APPARATUS FOR COATINGPAPER- Noel Obenshain and Wright M. Welton, Piedmont, W. Va., assignorsto West Virginia Pulp and Paper Company, New York, N. Y., a corporationof Delaware Application July 16, 1936, Serial No. 90,832

6 Claims.

Our present invention relates to methods of and apparatus for coatingpaper,

The coating of paper with suspensions of mineral pigments, to which thisapplication particularly applies, has presented serious problems for thereason that such suspensions commonly used in the paper art do not ofthemselves smooth out when applied with even slight irregularities. Whenthe paper is coated by a direct application of the coating liquidthereare formed, un-' less special precautions are taken, ripples orirregularities of the coating material on the paper which, when dried,produce streaks. Therefore, in much of the prior art practice, provisionis made for smoothing out the ripples or other irregularities formedupon application, either by the use of reciprocating brushes orof,smoothing or trowelling rolls. Such aids, however, have the drawbacksthat they are cumbersome and are responsible for a comparatively lowrate of output.

In view of these difficulties, proposals have been made to apply ameasured amount of coating material upon the travelling sheet of paperto be coated, in such manner as to produce an even coating in the firstinstance and thus obviate the use of subsequent smoothing devices. It isto this latter class of coating methods and apparatus that our presentinvention is directed, and it is a principal object thereof to devise a,new method and apparatus which will produce a coating of the usualmineral or other pigments having in a high degree the qualities ofsmoothness and uniformity, and in addition having the advantages of highoutput and reliability of operation.

' In carrying out our invention we make use of coating rolls having cutor formed therein a multitude of liquid receiving indentations orgroves, such rolls being preferably of metal and having the surfacethereof formed either by mechanical cutting or by photo engraving orother processes known to that art.

Our invention will be best understood by reference to the followingdetailed description taken with the annexed drawing in which:

Fig. 1 shows diagrammatically an arrangement of coating rollsconstituting a preferred embodiment of our invention.

Fig. 2 is a side view of same.

Fig. 3 is a view of a roll in which the grooves are of the screen type.

Fig. 4 is a view of a rollin which the grooves are of the inclinedparallel type.

Fig. 5 shows an arrangement for coating both sides of the paper in oneoperation; and

Fig. 6 is a side view of same.

In Fig. 1 the coating material is sprayed through pipe 9 upon thecoating roll l2 of the 5 type shown in Figs. 3 or 4 to be more fullyde-' scribed hereinafter. The excess coating is caught in pan Ill and ispumped therefrom back to the spray pipe a by means not shown.' Roll I2is driven from a source not shown and has in con- 10 tact therewith anoffset or applicator roll M which may be driven simply by contact withroll I! or preferably is positively driven by means of gears l3 and Bashown in Fig. 2 which operate to-drive said rolls at the same surfacespeed. The coating material fills to excess the multitude of pockets orgrooves in the surface of the roll l2 and a portion of the liquid sopicked up is transferred to the offset roll I4, which has a resilientsurface as of rubber, the excess coating being squeezed out by-thecontact or nip between rolls l2 and I4, so that roll l4 acquires auniform amount of coating for each contact with the roll I! without theuse of a doctor roll or blade. The

so-coated surface of the roll 14 then is brought v in contact with thepaper web l6 which passes over the roll l4 and is held in properjuxtaposition with respect to roll l4 by means of the guide rolls I1, I8 and I9. As revealed by Fig. 1, the transfer or offset roll l4 moves ina direction reverse to the travel of the web I6. I Various factorsgovern the uniformity of coating. imparted to the web l6.' One of theseis the amount of slip between the web and the offset roll H. Forconvenience this slip may be reckoned as the algebraic differencebetween the speeds of the web and the roll l4 divided by the speed ofthe paper and multiplied by 100 to give a percentage ratio, a directionof rotation of the roll reverse to the web being considered 40 negative.Thus far we have found'that satisfactory results are had when thepercent slip for the arrangement of Fig. 1 is between 200 and 450. Theseconditions, for example, will be fulfilled when the paper has a speed of500 feet per minute and the roll a speed in reverse of the paper of 600feet per minute, thereby giving a percent slip of 220. Another-factor isthe nature and frequency of the markings on the roll I2. Good resultshave been obtained when a screen marking has been used of a frequencyof- 25 to lines per inch, such a rollbeing shown in Fig. 3. The use ofthe parallel line marked roll of the type shown in Fig. 4 has givenresults as good as, if not better than, those obtained .with the .Jorychoosing rollsfof the; axis of the cylinder. "-Thenumberof lines perinch may-vary from 25 =to' l50'more or less "with a groovetofwa'llthickness {ratiobf fmm3 to 1 to 4 to 1; it beingunderstood that theabove i figures are given by way of example without limiting theinvention to any exact size orarrangement of markings. The indentedrolls may} desirably be made of copper or other non-corrod- 7 ing metal,and if deslredmay be cromium plated. Non-metallic indented rolls mightalso be em-v ployed. Such rolls in generalmay be made in a'mannersimilan to the manufacture of the in .taglio cut rolls used inrotogravure printing, The

amount of coating applied may be. best regulated either by varyingtheconsistency of the coating varying depth of cut-or by varying both thesefactors.

Thus .far when using the usual mineral pigments or fillers wehaveobtained superior results by driving the offset roll in a directionreverse to the travel of the paper, in comparison with those especiallywhen using coating compositions having greater coating or spreadingpower than those. 30

obtained by driving the offset roll in the same di- J rection as thepaper. 7 However, in some instances satisfactory results may be had whendriving the offset roll inthe same direction with the paper,

through a drying chamber, as is common'in the art.

In lieu of spraying the coating upon the indented roll, as by the spraypipe 9, the composition may be fed to the pan l and the latter aroundthe applicator roll. variations in the degree of slip have very littleraised so as partially to immerse the roll l2.

The improved method and apparatus described in'the foregoing is adaptedto be used with a variety of paper coating compositions. Typicalcompositions containing in suspension the usual mineral fillers orpigments are as follows:

(1) Chalk 100 parts Casein 15 to 18 parts Water added to ve 35% solidsThe mixture is then ground through a 3 roll ink grinder, diluted to 25%solids and re-ground.

(2): Clay 500 parts Satin white 850 Chalk 150 Cas 215 Water added togive 20% solids and suitably ground. By varying the amountof solids insuspension and the depth of grooving on the indented rolls as aforesaid,coatings of the type of the above examples have been successfullyapplied ranging from .3 pound to 10 pounds per ream per' side.

This amount of coating seems not to vary appreciably with the degree ofwrap of the paper Furthermore, slight effect on the amount ofcomposition applied. The

'I Yscreen' markingQ-Y the the 25 have aj'pitch of approximately 30'degrees-to paper at a surface speed as low as100 to as high as 500ffeetper minute;

Our improved method and apparatus may be used to coat paper; previouslyformed and dried, 'or'it may be used to coat the paper while the latteris in the paper making machine and before the web hasvbeen fully dried.t ,In'the claims, by "paper is'meant to include cardboard or pasteboardor other paper products which it may be desired to coat.

. V arious changes from the detailed description and specific data abovegiven will occur to those .skilled inthe art, without, however,departing from the'spirit of theinvention or the scope of the appendedclaims. Weclaim:

= 1. The method of coating a "web of paper or,

the like, whlchfcomprises applying a coating comv position comprisingmineral pigments to a cylindrical surface having a multitude of liquidreceiving indentations serving to hold a measured quantity of suchcomposition, transferring a portion of said coating so appliedto asecond surface having resilient properties by maintaining said surfacesin rolling contact whereby said resilient surface receives a uniformamount of coating composi- -,tion' whichis less than the amountinitially present on said surface having indentations, then.

contacting said resilient surface with a web o paperor the like movingwith respect to said resilient surface so as to occasion a substantialslip betweensaid vweb and said contacting surface, while maintainingsaid Web free to move slight amounts incident to variations in diameterand position of said resilient cylindrical surface. 2. The methodaccording to claim 1 in which said slip varies from 200% to 500%. v 3.The method of coating a web of paper or the like, which comprisesapplying a coating compositioncomprising mineral pigments to acylindrical surface having a multitude of liquid receiving indentations,transferring a portion of said coating so applied to a second surfacehaving resilient properties by maintaining said surfaces in rollingcontact whereby said resilient surface receives a uniform amount ofcoating composition which is less than the amount initiallypresvariations in diameter and position of said resilient cylindricalsurface.

4. In a device adapted for coating paper with a liquid suspension offinely divided mineral pigments or fillers, a roll comprising acylindrical surface having a multitude of liquid receiving indentations,means for supplying the coating composition to said roll, a resilienttransfer roll receiving coating from said indented roll and applyingsame to a paper web, means for driving said transfer roll in reversedirection to thetravel of said web, guide rolls for passing the paperover said transfer roll, said guide rolls being disposed so as to permitthe paper tomaintain contact with thetransfer roll regardless of minutevariations in' the position of said.roll.

5. In a device adapted-for coating paper with a liquid suspension offinely divided mineral pigments or fillers, a roll comprisinga-cylindrical surface of relatively hard material having liquidreceiving indentations of a frequency from 25 to improved process hasthus far'ienabledus to coat per inch, means for supplying the coating 5rotating in contact with said indented roll and receiving coating fromsaid indented roll and applying said coating to a paper web, and meansfor driving said transfer roll in reverse direction to the travel ofsaid web. a

6. In a-device adapted for. coating paper with a liquid suspension offinely divided mineral pigcomposition to said roll, a resilient transferroll w a a a, 2. 9 .92

composition to said roll, a resilient transfer roll receiving coatingfrom said indented roll and applying same to a paper web, means fordriving said transfer roll in reverse direction to the travel of saidweb, and means for driving said indented roll and said transfer roll atsubstantially the same surface speed, guide rolls for passing the paperover said transfer roll, said guide rolls be-

